Flow directed catheters are designed so that the flow of blood through an artery directs the catheter tip along the arterial flow path and to the target site. One type of flow directed catheter uses an enlarged balloon or cup-shaped end to create a partial obstruction causing the blood flow to pull the tip of the catheter in the direction of the blood flow. See, for example, U.S. Pat. Nos. 3,995,623 to Blake et al. and 4,024,873 to Antoshkiw et al.
Another type of flow directed catheter has a very flexible distal end which is designed to be carried along by the blood flow instead of by partially blocking the artery. One of this type is manufactured by Balt S. A. of France under the trademark Magic; it is made of a hydrophobic material with a relatively stiff proximal section, a moderately flexible midsection and a quite flexible distal section. While this catheter has enjoyed some success, it has several shortcomings. The material from which the distal section is made is quite stretchable, elongates readily and has a relatively low bursting strength. This can be a problem since if a portion of the distal section breaks off from the remainder of the catheter, the broken-off portion could be left inside the vessel to cause further damage. The inside diameter of the distal section is quite small and is often not usable with a guide wire. If a guide wire is used the guide wire tends to pull on and stretch the distal section and damage the floppy tip; a guidewire could also puncture the wall of the distal section as well. These problems are due to the material from which the distal end is made. The material dictates that in order to get the desired suppleness, the distal section must have a small diameter, such as an outside diameter of 0.025 inch (0.64 mm or 2 French) and in inside diameter of 0.015 inch (0.38 mm). The small inside diameter limits the compatibility of therapies. For example, it is quite difficult, if not impossible, to inject occlusion devices such as polyvinyl alcohol (PVA) particles, metal coils, gelfoam or silk sutures with such small diameter catheters.
Another prior art flow directed catheter is manufactured by Target Therapeutics of Fremont, Calif. and is sold under the trademark Zephyr. It is intended to be used with a wire or mandrel which allows the stiffness of the midsection to be varied. The Zephyr has a lubricious, hydrophilic coating on its outside surface to aid passage of the catheter through the guiding catheters and vessels. A problem with this catheter is that it suffers from the similar limitations of the Magic catheter due to its small diameter. Also, this catheter is too stiff to access distant vascular structures. See U.S. Pat. No. 5,336,205 for Flow Directed Catheter.